The Evaluation And QTL Mapping For Pre-harvest Sprouting Tolerance In Rice Germplasm

Rice is an important food in our country,its yield and quality are closely related to standard of people's living.The phenomena of germination on the parent plant,usually due to the long spell of rainy weather or the conditions of high temperature and humidity before harvest,was termed as pre-harvest sprouting(PHS).PHS on the rice seriously affects the yield,quality,storage and seed value,which is widely concerned by breeding workers and agricultural producers.There are many internal factors affecting rice PHS,such as dormancy level,endogenous hormones,moisture content of seeds,etc.And there also are environmental factors such as temperature,moisture and light.The sprouting phenotypes of different cultivars are rich in variation.Screening out extreme varieties with PHS tolerance is helpful to cultivate varieties with hight PHS tolerance and provide the germplasm resources foundation for the research of PHS tolerance in rice.This research includes two parts.one is to evaluated the PHS of a batch of conventional photo-sensitive japonica in Zhejiang province,and screened the germplasm with high PHS tolerance by using the indexes that could evaluate PHS tolerance.The second is to construct the genetic linkage map derived from the F2 population of the Nipponbare and the Guiyin 206,for locating the QTL to look for genes associated with PHS in rice and to understand the genetic mechanism of PHS.We made some progress in the research:1.In Hainan base,161 photo-sensitive japonica varieties were planted to screen varieties with PHS tolerance,and 67 varieties were selected for further identification in Hangzhou.Among 67 varieties with three heading types,the earlier the heading stage,the higher the average germination rate at 20 d,30 d and 40 d after heading.In contrast,the later the heading stage,the higher the average germination rate at 60 d after heading.For the same heading stage,the average germination rates at 20 d,30 d,40 d and 60 d after heading were gradually increased.Through correlation analysis we found that there was a significant positive correlation among the five indicators of spike germination rate at 30 d,40 d and 60 d after heading,grain germination rate and sprouting rate of Hainan corresponding cultivars,which could better reflect the different PHS tolerance among different varieties and could be used as a reference standard for screening germplasm with PHS tolerance.We got six varieties with high PHS tolerance including the Chunjiang 162,Zhongjing 6,Shaojing 15-28,Shaojing 18,ZH13-96 and R1133.At the same time we got six varieties with low PHS tolerance including Jia 14-85,ZH13-15,Chunjiang 157,Jia 11-55,Shaonuo 14-40 and Shaonuo 03-27.All These varieties made the foundation for the breeding the varieties with high PHS tolerance in the future.2.The sprouting rates of 94 individuals and parents of F2 segregating population of Nipponbare× Guiyin 206 were measured.The results showed that the parent Nipponbare had a higher sprouting rate than the parent Guiyin 206,which were 21.69%and 2.05%,respectively on the 7th day under 30? culture.The sprouting rates of 94 individuals of F2 population on the 7th day under 30 ? culture showed a continuous distribution and showed a large bi-directional super-progeny separation with the characteristics of quantitative trait inheritance.A genetic linkage map of rice was constructed using the SSR tag,which included 101 SSR tags and a total length of 1840.97 cM.And the average genetic distance between the tags is 18.2 cM.With the phenotypic and genotype data from F2 population we used the QTL IciMapping software to detect a total of four QTLs that were associated with PHS(qPHS2,qPHS4,qPHS5 and qPHS12)and located in 2,4,5 and 12 chromosome respectively.The phenotypic variations explained were ranged from 3.96%to 58.19%,in which qphs12 had the higher effect value.Favorable alleles were contributed for the qPHS4 by Nipponbare,while favorable alleles were contributed for the other three QTLs by Guiyin 206.That laid the foundation for the follow-up gene fine mapping and cloning.